1. Field of the Invention
The present invention relates to a device for monitoring corrosive environment and a method for monitoring corrosive environment, both targeting an indoor environment, mainly an environment installed with electric and electronic apparatuses. A level of corrosion generated by a corrosive gas present in the environment is measured by the device and method for monitoring corrosive environment.
2. Related Art
Japanese Unexamined Patent Application Publication No. 2003-294606 (i.e., Patent Document 1) discloses background art of the invention. That is, the environment evaluation apparatus of Patent Document 1 basically includes 1) an element unit for reacting with gas components in an environment, 2) a unit for detecting a change in the element unit and converting the detected change into an electric signal, and 3) a storage unit for storing the detected data. Specifically, the element unit is formed by using a plurality of metal films, for example, a metal film with a thickness of 0.1 μm made of silver, copper, iron, and stainless steel. Herein, evaluating a material in an environment is performed by measuring a time course of at least one property selected from the light reflection, light transparency and electric resistance of the metal film, thereby detecting gas components in the environment.
When the time course of the electric resistance value is measured, a change in the electric resistance value caused by the change in the whole metal film (e.g., entire surface corrosion) may be measured. This measurement allows a thickness of the corroded metal film to be calculated, thereby to easily afford a corrosive rate thereof.
Note that a gas detection system detects a change in an element, and converts the detected change into an electric signal. The gas detection system includes a gas introduction unit and a gas detection element (i.e., corresponding to the sensor unit of the present invention). Those gas components are guided to the gas detection element by a suction pump of the gas introduction unit. As mentioned above, under circumstances as the global environment changes, it is advantageous to provide a measuring apparatus greatly useful for evaluating various materials located in such environment.
Here, long term reliability is required for electric and electronic apparatuses in order to stably operate target equipment. Further, a lot of electric and electronic components, which include a fine wiring structure and a film plating structure both applied with a high density mounting structure, are mounted on the target equipment to achieve high speed operation and space-saving arrangement. In those electric and electronic components, even slightly corroded damage may change the electric property or magnetic property of the components to cause a failure or malfunction. Therefore, suppression of the corroded damage is an important issue to improve the reliability of the electric and electronic apparatuses. Eventually, continuous evaluation in easy, a short period and high accuracy of corrosive environment installed with electric and electronic apparatuses is demanded to reflect anti-corrosion measures associated with a corrosion level of the environment onto the design and maintenance of those apparatuses
Meanwhile, according to the ISO11844-1 standard, a method for evaluating a corrosion level of copper, silver, aluminum, iron and zinc which are exposed for a predetermined period under an corrosive environment is generally utilized, as a tool for evaluating corrosiveness of the environment installed with electric and electronic apparatuses. It has been well known that copper, silver, aluminum, iron and zinc corrode by such corrosive gases as SO2, NO2, H2S, although a corroded degree of each metal is different each other.
However, the method for evaluating environment and the device using the method in the above conventional technique have the following problems. That is, if an evaluation target is the environment with “a middle level of corrosiveness” in which a failure in electric and electronic apparatuses may occur due to the corrosiveness degree described in the ISO11844-1 standard and a silver film with a thichness of 0.1 μm. (i.e., 100 nm) is used for measuring the time course of the electric resistance value., a detection sensor using such a silver film is merely applicable to the measurement only for about one month. Herein, according to the ISO11844-1 standard, the above middle level of corrosiveness is the environment where a corrosive rate of the exposed silver falls in the range from 105 to 410 nm/year.
Further, if an evaluation target is the environment with “a high level of corrosiveness or “an extremely high level of corrosiveness”, a measurable period of the detection sensor becomes shorter than one month. Herein, the environment with the “high level of corrosiveness” is the environment where probability of causing corrosion to influence the reliability of the devices is high, and improvement of the environment is essential, more specifically, where a corrosive rate of the exposed silver falls in the range from 410 to 1050 nm/year. The environment with the “extremely high level of corrosiveness” is the environment where a corrosive rate of the exposed silver falls in the range from 1050 to 2620 nm/year. Accordingly, the above type of detection sensor is not suitable for the long term measurement.
In the meantime, if a thickness of the silver film is elongated, a detection sensor using the elongated film may have a long measurable period. However, this procedure has a drawback that uniformness of the thickness of the film becomes larger as the thickness thereof becomes thicker, which results in deterioration of the measuring accuracy.
Moreover, the method for evaluating environment and the device using the method in the above conventional technique have additional problems. That is, if local corrosion occurs in the sensor unit, more specifically, if dust or salts adheres to the sensor unit and corrosion occurs in the vicinity of the adhering portion, the corrosion makes a measurable period of the sensor unit turn to shorter than the original period essentially provided for the sensor unit.
Furthermore, if a sensor unit (i.e., gas detection element) is directly exposed to the target environment, a corrosive rate varies depending on a flow rate of the corrosive gas present in the target environment, leading to another problem.